Pneumatic screw-drivers

ABSTRACT

A pneumatic screw-driver comprises a casing having a pneumatic motor housed in the rear part of the casing and a screw-driver spindle rotatably mounted in the front or nose of the casing. The rotor of the pneumatic motor is integral with a cup-shaped flywheel which projects forwardly to a position adjacent the spindle. The spindle has a radial lug on its rear end and a shaft secured to the spindle coaxially therewith projects rearwardly into the cup-shaped flywheel and is also coaxial with the latter. A sleeve member is slidably mounted on the shaft and carries a striker which is rotatably mounted on the sleeve member and is rotated by the flywheel. The lug and striker are resiliently urged apart by a compression spring disposed on the shaft. The sleeve member has a cam on its rear face and a bush rotatably mounted on the shaft rearwardly of the sleeve member mounts a roller in a position such that it periodically engages the cam and thereby reciprocates the striker and causes the latter periodically to strike the radial lug on the spindle so as to impart screwing impulses to the spindle. The bush is rotated by the rotor through a reduction gear mechanism which is coupled to the rotor by a shaft which serves as a torsion bar and absorbs torsional stresses. The casing includes a pistol grip having a trigger-actuated valve for controlling the admission of compressed air to the pneumatic motor.

United States Patent [1 1 Leoni Oct. 30, 1973 PNEUMATIC SCREW-DRIVERS [75] Inventor: Primo Leoni, Reggio Emilia, Italy [73] Assignee: Nuova L.A.P.I., Reggio Emilia, Italy [22] Filed: July 28, 1972 [21] Appl. No.: 275,979

Primary ExaminerMarvin A. Champion Assistant Examiner-William F. Pate, III Attorney-Joseph F. Brisebois et al.

[57] ABSTRACT A pneumatic screw-driver comprises a casing having a 1r 94056/ F/l/FZI/ pneumatic motor housed in the rear part of the casing and a screw-driver spindle rotatably mounted in the front or nose of the casing. The rotor of the pneumatic motor is integral with a cup-shaped flywheel which projects forwardly to a position adjacent the spindle. The spindle has a radial lug on its rear end and a shaft secured to the spindle coaxially therewith projects rearwardly into the cup-shaped flywheel and is also coaxial with the latter. A sleeve member is slidably mounted on the shaft and carries a striker which is rotatably mounted on the sleeve member and is rotated by the flywheel. The lug and striker are resiliently urged apart by a compression spring disposed on the shaft. The sleeve member has a cam on its rear face and a bush rotatably mounted on the shaft rearwardly of the sleeve member mounts a roller in a position such that it periodically engages the cam and thereby reciprocates the striker and causes the latter periodically to strike the radial lug on the spindle so as to impart screwing impulses to the spindle. The bush is rotated by the rotor through a reduction gear mechanism which is coupled to the rotor by a shaft which serves as a torsion bar and absorbs torsional stresses. The casing includes a pistol grip having a triggeractuated valve for controlling the admission of compressed air to the pneumatic motor.

6 Claims, 4 Drawing Figures PNEUMATIC SCREW-DRIVERS The present invention relates to pneumatic screwdrivers and other pneumatic torque-applying devices of the type comprising internally an inertial mass which intermittently engages or strikes a screwing spindle and is rotated by a compressed air motor, preferably, of the bladed type. More particularly, the invention relates to automatic pneumatic screw-drivers of this type in which the compressed air motor comprises at least two thrust chambers so as to permit a reduction in the total size of the device.

An object of the present invention is to provide a pneumatic screw-driver or other pneumatic torqueapplying device which, although of small size because of the use of a compressed air motor with two thrust chambers, is of high screwing or turning efficiency. A further object of the invention is to provide such a device, which comprises built-in safety devices for avoiding brittle fractures due to the successive impacts to which the inertial operating mass, rotating at high velocity, is subjected without it being necessary to increase the size of the device.

According to the present invention, a speed reduction mechanism to provide between the pneumatic motor and the drive for a reciprocating striker part of the rotating inertial mass so that the striker reciprocates at a slower frequency thanthe speed of the motor, thereby to decrease the rate of the impulses transmitted by the striker to the output spindle of the device, and hence enable the motor, during the increased intervals of time between one impulse and another, to acquire a higher speed, so that it is able to transmit a greater quantity of kinetic energy at the moment of impact with the spindle. In this manner the effect obtained is the same as that which would be achieved by increasing the weight of the inertial mass, without however negatively affecting the size and weight of the complete device.

So as to obviate the greater mechanical stresses to which the machine members, which maintain their original small size, are subjected, according to a feature of the invention, the drive between the motor and an input gear of the reduction mechanism comprises a drive shaft of suitable dimensions so as to function as a torsion bar and give the system the necessary elasticityduring the impact phases, in this way avoiding brittle fractures.

in order that the present invention may be more readily understood, reference will now be made tothe accompanying drawings, in which:

FIG. 1 is an axial section through a pneumatic screw- FIG. 3 is a perspective view of the roller carrying bush; and

FIG. 4 is a perspective view of the torsion shaft.

Referring to the drawings, the pneumatic screwdriver drivercomprises a casing 1 having a pistol-grip 1a. Housed in the rear part of the casing is a radial bladed pneumatic motor having two thrust chambers. The rotor 2 of the motor has a cup-shaped flywheel 3 projecting forwardly of the rotor and located in front of this flywheel, coaxially therewith, is a spindle 4 for receiving a screw-driver tool (not shown). The rotor 2 and flywheel 3 are rotatably mounted within the casing by rolling bearings 41, 42 and a thrust bearing 43. The

spindle 4 is rotatably mounted in the nose 44 of the casing in a rolling bearing 45 housed in a bearing bush 46 secured to the nose.

Disposed at the rear end of the spindle 4 is a radial lug or coupling piece 40 which co-operates with a striker mass 5 disposed rearwardly of the spindle and torsionally engaged in a slot in the front end of the cupshaped flywheel 3. The latter is freely rotatable on a support sleeve 6, which is axially slidable on a grooved shaft 8, and has a raised cam 7 on its rear face. The shaft 8 is located coaxially between the rotor 2 and the spindle 4 and is fixed to the spindle. A strong compress'ion coil spring 9 is located around the shaft 8 between the striker 5 and the spindle 4 so as to urge them apart, and the annular member 10, against which the spring presses, retains the striker in its seat on the sliding sleeve 6.

The grooved shaft 8 extends rearwardly to a position adjacent the rotor 2 and terminates at its rear end in an annular flange 11 which supports three double pinions 12 which are symmetrically disposed about the flange and are freely rotatable with respect to the flange. The front ones of these double pinions individually mesh with a gear wheel 13 connected to the rear of a bush 14 which is, itself, rotatably mounted on the grooved shaft 8 in a position between the flange 11 and the sliding sleeve 6. Rotatably mounted on the front face of this bush on a radial pin 15a supported between two part-cylindrical bosses 15b on the front face is an actuating roller 15 which co-operates with the cam 7 on the sliding sleeve 6 in order periodically to cause the striker to engage the lug 40 of the spindle 4.

Another slender shaft 16 is mounted coaxially within the rotor 2. The rear end of this shaft 16 is keyed to the rotor whilst the forward end 16b is supported in a cylindrical bearing recess 17 formed coaxially in the adjacent end of the shaft 8 and serving as a rotary support. To the same end 16b of the shaft is keyed a gear wheel 18 which simultaneously meshes with the three rear pinions of the double pinions 12 so as to rotate the bush 14 through a predetermined gear ratio; Fixed to the flange 11 symmetrically between the double pinions 12 are rivets 19 which, via spacers 20, locate a rear retainer ring 21 which retains the double pinions in their bearings in the flange 11.

The device operates as follows. Compressed air for driving the pneumatic motor is admitted to the motor via a passageway 47 under the control of a valve 48 actuated by aflnger trigger 49 pivotally mounted in the pistol grip 1a of the screw-driver. When compressed air is admitted,the rotor 2 drives the flywheel 3, and hence the striker 5, and also drives the shaft 16 which rotates the bush 14 via the gear wheels and pinions 18, l2-and 13. Rotation of the bush 14 causes the roller 15 periodically to engage the cam 7 for short periods thereby recip rocating the sleeve 6 and the striker 5. During each forward stroke of the striker, it strikes the lug 40 and, consequently, imparts a screwing or turning impulse to the spindle 4, the reaction due to the impulse being absorbed by the elastic torsion of the shaft 16. The frequency of the screwing pulses is determined by the speed of rotation of the rotor 2 and the transmission ratio of the reduction gear mechanism 12, 13 and 18. If the gear wheel 18 and the rear ones of the double pinions 12 have the same number of teeth and, if the gear 13 has a number of teeth double that of the front pinions 12, then the striker 5 imparts a blow'to the lug 40 once every two revolutions of the rotor 2. This is the case with the embodiment described above.

From an examination of the Figures and the preceding description, the particular strength of the device will be evident, as will be the important function of the shaft 16, i.e., because of the high elasticity resulting from its slenderness, it is able elastically to absorb by torsion the impacts transmitted by the spindle 4 to the reduction gear'mechanism, via the grooved shaft 8, during the transmission cycles of the screwing impulses.

Whilst a particular embodiment has been described, it will be understood that various modifications can be made without departing from the scope of the invention as defined by the appended claims.

I claim:

1. ln a pneumatic torque-applying device which is operable, preferably in both directions of rotation, by a pneumatic motor, and in which the rotor of said pneumatic motor rotates an inertial mass driving a striker which intermittently engages co-operating means on the output spindle of the device, the improvement comprising a shaft disposed coaxially relative to said inertial mass and secured to said output spindle of the device, sleeve means slidably mounted on said shaft and having cam means thereon, means rotatably mounting said striker on said sleeve means, rotatable actuating means co-operating with said cam means to effect reciprocation of said sleeve means and thereby periodic engagement of said striker with said co-operating means on said spindle, a speed reduction mechanism coupling said rotor to said actuating means so that said actuating means rotates at a reduced speed relative to said rotor, and hence said inertial mass and striker, and coupling means connecting said reduction mechanism to said rotor in a substantially elastic manner.

2. A device as claimed in claim 1, in which said inertial mass comprises a cup-shaped flywheel projecting forwardly from said rotor and having means at its free end engaging said striker for rotating same, said shaft is disposed coaxially with said spindle and is secured to said spindle so as to project rearwardly thereof, said actuating means includes a bush rotatably mounted on said shaft rearwardly of said sleeve means, said shaft has an end flange rearwardly of said bush supporting gear means of said reduction mechanism which couples said rotor to said bush so as to cause one complete revolution of said bush for each two or more revolutions of said rotor, said coupling means is located coaxially within said rotor for elastically absorbing torsional impacts, and cam operating means is located on said bush for causing axial reciprocation of said sleeve means to an extent sufficient to cause said striker to strike said co-operating means on said spindle so as to impart to said spindle an intermittent rotational impulse.

3. A device as claimed in claim 2, in which said gear means controlling the rotation of said bush comprises a plurality of double pinions freely rotatable in said flange and disposed at symmetrically spaced positions around the axis thereof, the forward pinions of said double pinions individually meshing with a gear wheel connected to said bush, and a retainer ring retaining said double pinions in position on said flange disposed coaxially with respect to said shaft and fixed to said flange by pins symmetrically disposed between said double pinions, each pin having an appropriate spacer between said ring and said flange.

4. A device as claimed in claim 3, in which said coupling means comprises a second shaft located coaxially within said rotor and havng its rear end keyed to said rotor and its front end freely supported in a bearing seat formed in the adjacent end of said first-mentioned shaft, a gear wheel connected to said second shaft and meshing simultaneously with the rear pinions of said double pinions, said second shaft being so shaped and being made from such a material as to have a degree of elasticity sufficient to function as a torsion bar for cushioning the impact due to the transmission of the turning impulses produced by said striker.

5. A device as claimed in claim 3, in which said actu ating means includes a radial pivot pin supported between part-cylindrical enlargement on the front face of said bush, a roller mounted on said pivot pin at such a position and projecting forwardly by such an amount as to cause it to engage said cam on the adjacent face of said sleeve means so as to cause axial reciprocation of said striker supported by said sleeve through a predetermined stroke.

6. A pneumatic screw-driver device as claimed in claim 1, comprising a main casing having a pistol grip, a radial-bladed pneumatic motor having one or more thrust chambers disposed in the rear of said casing and controlled by a two-way distributor, said motor including a rotor integral with a cup-shaped flywheel projecting forwardly of said rotor, a spindle for receiving a screw-driver tool rotatably mounted in the casing in front of said flywheel and having a radially extending lug at its rear end adjacent the flywheel, a grooved shaft secured to said spindle coaxially therewith and projecting coaxially within said flywheel, a sleeve member slidably mounted on said shaft and having a cam on a rear face thereof, a striker rotatably mounted on said sleeve member and engaged in a slot in said flywheel, a compression coil spring disposed on said shaft between said spindle and said sleeve member and urging said lug and striker apart, a bush rotatably mounted on said shaft rearwardly of said sleeve member and mounting a roller adapted to engage said cam on said sleeve member, thereby to effect reciprocation of said striker and intermittent engagement thereof with said radial lug on said spindle, a coaxial gear wheel integral with the rear face of said bush, an end flange on said shaft rearwardly of said gear wheel, three double pinions rotatably mounted on said flange at symmetrical positions therearound, the front ones of said double pinions individually meshing with said gear wheel of said bush, a drive shaft disposed coaxially within said rotor and having a rear end coupled to said rotor and a front end freely rota'table in a bearing recess in the adjacent, rear end of said grooved shaft, a gear wheel secured to said drive shaft adjacent the front end thereof and simultaneously engaging the rear ones of said double pinions, passage means for supplying compressed air to said motor, valve means located in said pistol grip and controlling the admission of air pressure to said passageway means, and a finger trigger pivotally mounted on said pistol grip for actuating said valve means to admit compressed air to said passageway means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,7 ,577 Dated October 30, 1973 Inventor(s) PRIMQ LEONI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[30] I I Foreign Ap lication Priority Data Italy-0o... 00.000 April 13, 1972 ItaIy............. 4685 -l-A/72 signed and sealed this 16th day of July 197A.

(SEAL) Attest:

MCCOY M. GIBSON, JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents po'wso noss) USCOMM-DC scan-Poo fi U S. GOVERNMENT PRINTING OFFICE: 19! O-366334. 

1. In a pneumatic torque-applying device which is operable, preferably in both directions of rotation, by a pneumatic motor, and in which the rotor of said pneumatic motor rotates an inertial mass driving a striker which intermittently engages cooperating means on the output spindle of the device, the improvement comprising a shaft disposed coaxially relative to said inertial mass and secured to said output spindle of the device, sleeve means slidably mounted on said shaft and having cam means thereon, means rotatably mounting said striker on said sleeve means, rotatable actuating means co-operating with said cam means to effect reciprocation of said sleeve means and thereby periodic engagement of said striker with said cooperating means on said spindle, a speed reduction mechanism coupling said rotor to said actuating means so that said actuating means rotates at a reduced speed relative to said rotor, and hence said inertial mass and striker, and coupling means connecting said reduction mechanism to said rotor in a substantially elastic manner.
 2. A device as claimed in claim 1, in which said inertial mass comprises a cup-shaped flywheel projecting forwardly from said rotor and having means at its free end engaging said striker for rotating same, said shaft is disposed coaxially with said spindle and is secured to said spindle so as to project rearwardly thereof, said actuating means includes a bush rotatably mounted on said shaft rearwardly of said sleeve means, said shaft has an end flange rearwardly of said bush supporting gear means of said reduction mechanism which couples said rotor to said bush so as to cause one complete revolution of said bush for each two or more revolutions of said rotor, said coupling means is located coaxially within said rotor for elastically absorbing torsional impacts, and cam operating means is located on said bush for causing axial reciprocation of said sleeve means to an extent sufficient to cause said striker to strike said co-operating means on said spindle so as to impart to said spindle an intermittent rotational impulse.
 3. A device as claimed in claim 2, in which said gear means controlling the rotation of said bush comprises a plurality of double pinions freely rotatable in said flange and disposed at symmetrically spaced positions around the axis thereof, the forward pinions of said double pinions individually meshing with a gear wheel connected to said bush, and a Retainer ring retaining said double pinions in position on said flange disposed coaxially with respect to said shaft and fixed to said flange by pins symmetrically disposed between said double pinions, each pin having an appropriate spacer between said ring and said flange.
 4. A device as claimed in claim 3, in which said coupling means comprises a second shaft located coaxially within said rotor and having its rear end keyed to said rotor and its front end freely supported in a bearing seat formed in the adjacent end of said first-mentioned shaft, a gear wheel connected to said second shaft and meshing simultaneously with the rear pinions of said double pinions, said second shaft being so shaped and being made from such a material as to have a degree of elasticity sufficient to function as a torsion bar for cushioning the impact due to the transmission of the turning impulses produced by said striker.
 5. A device as claimed in claim 3, in which said actuating means includes a radial pivot pin supported between part-cylindrical enlargement on the front face of said bush, a roller mounted on said pivot pin at such a position and projecting forwardly by such an amount as to cause it to engage said cam on the adjacent face of said sleeve means so as to cause axial reciprocation of said striker supported by said sleeve through a predetermined stroke.
 6. A pneumatic screw-driver device as claimed in claim 1, comprising a main casing having a pistol grip, a radial-bladed pneumatic motor having one or more thrust chambers disposed in the rear of said casing and controlled by a two-way distributor, said motor including a rotor integral with a cup-shaped flywheel projecting forwardly of said rotor, a spindle for receiving a screw-driver tool rotatably mounted in the casing in front of said flywheel and having a radially extending lug at its rear end adjacent the flywheel, a grooved shaft secured to said spindle coaxially therewith and projecting coaxially within said flywheel, a sleeve member slidably mounted on said shaft and having a cam on a rear face thereof, a striker rotatably mounted on said sleeve member and engaged in a slot in said flywheel, a compression coil spring disposed on said shaft between said spindle and said sleeve member and urging said lug and striker apart, a bush rotatably mounted on said shaft rearwardly of said sleeve member and mounting a roller adapted to engage said cam on said sleeve member, thereby to effect reciprocation of said striker and intermittent engagement thereof with said radial lug on said spindle, a coaxial gear wheel integral with the rear face of said bush, an end flange on said shaft rearwardly of said gear wheel, three double pinions rotatably mounted on said flange at symmetrical positions therearound, the front ones of said double pinions individually meshing with said gear wheel of said bush, a drive shaft disposed coaxially within said rotor and having a rear end coupled to said rotor and a front end freely rotatable in a bearing recess in the adjacent, rear end of said grooved shaft, a gear wheel secured to said drive shaft adjacent the front end thereof and simultaneously engaging the rear ones of said double pinions, passage means for supplying compressed air to said motor, valve means located in said pistol grip and controlling the admission of air pressure to said passageway means, and a finger trigger pivotally mounted on said pistol grip for actuating said valve means to admit compressed air to said passageway means. 